This takes place for the following reason:
In your case end_date is 2018-05-10. So it means that your event finishes May 20th at 00:00 and covers May 9th and don’t cover May 10th. If you want to fully cover May 10th you should set end date “2018-05-11” or “2018-05-11 00:00”. Maybe you could at least use “2018-05-10 23:59:59”, but correct case is to use “2018-05-11” or “2018-05-11 00:00”.
If it necessary for you, you could correct event dates in onTaskLoading handler. docs.dhtmlx.com/gantt/api__gantt … event.html
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